Malaria, the world's most deadly parasitic disease, afflicts 300-500 million people and causes 1-2 million deaths annually. The emergence of drug resistant parasites, primarily Plasmodium falciparum, has eroded the efficacy of all currently available chemotherapeutic agents. In addition to diminished utility, existing agents lack chemical diversity and have limited--4 to 6-biological targets. An ideal new antimalarial agent should be highly active, specific for P. falciparum and must show activity against multi-drug resistant (MDR) strains. Previously, we have identified high activity small molecules or "screening positives" that inhibit growth of or are toxic to P. falciparum in our whole-cell high-throughput screen (HTS) by screening structurally diverse small molecule libraries. The whole-cell method is optimal in phenotypic assays since it will allow all relevant blood-stage targets to be screened simultaneously and will assure that screening positives have desirable pharmacokinetic properties such as cell permeability, active in the context of the cell environment and exhibit some degree of specificity in their biological actions. Our next step in discovering new chemotherapeutic agents is to characterize the biological activity of screening positives identified in our primary whole-cell HTS. This proposal outlines screens that are focused on finding inhibitors for specific biological activities that lead to parasite growth inhibition or death. We will develop a phenotypic-based HTS whole-cell assay to characterize invasion of the parasite into the host red blood cell, identify stage specific activity of the small molecule throughout the life cycle of the parasite, and killing multi-drug resistant parasites. To date, an invasion HTS for P. falciparum has not been reported in the literature. Identification of cellular factors involved in parasitic invasion and transmission at the host cell erythrocyte is critical for understanding parasitic pathogenesis and should aid in the development of effective chemotherapeutics.